Problem with query using a date range

Hi all,

I'm a relatively new ES user and I've run into an issue querying an index
with a date range attached.
The query returns data when I try it locally (ES version 0.19.8), but my
remote installation (on EC2 using version 0.19.12) won't return results.

I've recreated the index a number of times but I keep striking out.

I've created the following gist with the query in question as well as the
results returned when I omit the date range.

Any help on this would be great appreciated.